Of course manipulation is possible, and bad, but so are insinuations of manipulation without evidence, and the latter are (by every indication I've seen) orders of magnitude more common. That's why the site guidelines ask you not to post like this.
https://news.ycombinator.com/newsguidelines.html
https://hn.algolia.com/?sort=byDate&dateRange=all&type=comme...
In the long run, if manipulation ends up dominating forums like HN, the only real solution is to do what we ought to all be doing anyway: have a culture in which arguments are answered by better arguments. Since that's the only long-term immunity, we might as well develop it now.
Hopefully, a marketplace of ideas will be sufficient in practice here.
If I am to take the comment I need something that would give some credibility to it, like having some way to verify the claims or if that is not possible, have a real person that puts their word behind the claim.
There is a reason why it is not possible for anonymous witness to testify in court and the reason is that anonymous person can say whatever they want with no responsibility for their words. It is exactly that responsibility and accountability that gives credibility to the witness.
The damaging power of rumor comes from the fact that you can't tell whether the information is true or not, but you pass it anyway. The act of passing the rumor is already causing damage even if you don't act on the information in any other way.
For you this might seem innocuous but many people have been completely broken by a simple rumor and that's why I have always been taught that spreading or allowing to spread rumors is always a bad thing to do.
It's also true that such comments can be counterfeited, which is where this gets complicated. But HN would be worse off without that class of comments. It's a legit use for throwaway accounts.
Are they verifiable? I don't think that's the best standard to apply to internet comments. The vast majority aren't. You have to assess credibility, but I wouldn't call that verification. In the case of a throwaway account, the only public information for assessing credibility is the content of the comments themselves, but that's not all that different from the usual situation on the internet. Admins have it a bit easier because there is other data we can also look at.
If we can't, then can we proactively discourage bad actors a different way? Or somehow sufficiently right harm done and unjust advantage taken, after the fact?
That way if you got something important to say there is a backstory to verify.
Of course this can be gamed and personas can be built as a weapon for future conflicts but at least the option is available for me and you to communicate with some credibility without opening us up to offline attacks. (I was originally writing IRL, but online is Real Life IMO, it is just that some parts of my online life doesn't point back a single identity.)
There are a number of people here who run two accounts, like me. It is mostly a good thing IMO and totally OK with the mods as long as the alt accounts follow the rules and doesn't change too often. This is my third in a decade or so I think.